Gravity conduits in urban settings are widely used for conveyance of sewage and stormwater. They are designed to convey the peak flow rate under partially full flow conditions, while the actual day-to-day flow rate and depth of flow are substantially less.
Separate sanitary sewers experience daily peak flows during the hours of maximum water use and are designed to convey the peak flow at 50% to 85% of full flow depth. Separate sanitary sewers may also receive infiltration inflows from surrounding groundwater and during wet-weather conditions, which are accommodated for in the design to ensure partially full flow conditions during peak flows. Storm drains that collect wet-weather flows are designed to run nearly full during their particular design hydrological event, which on average occurs once every 2 to 10 years or longer depending on the return period of the design storm. Combined sewers that convey both sanitary and storm water are subject to both diurnal and wet-weather flows and are designed for just less than full flow for the combined peak flows.
Therefore, the full conveyance capacity of gravity pipes is grossly underutilized. The void space between the surface of the flowing water in a gravity conduit and the conduit perimeter above, known as the headspace, represents significant conveyance capacity, which is either never utilized or only utilized for a small percent of time during the life of the conduit. Given the increase in water conservation, the flow rates and depths in gravity conduits are decreasing making them increasingly more underutilized.
The increasing underutilization of conveyance capacity in gravity conduits coincides with increasing need for conveyance of locally developed water resources, such as recycled water and captured storm water. Many cities are embarking on extensive and costly pipeline construction projects to convey and distribute recycled water in purple-colored pipes to replace and offset freshwater use. Given the often-congested urban setting of these projects, they face alignment, environmental, and permitting challenges that make many such projects infeasible and cause significant delays and increased costs.
Therefore, there is a need for a simple and practical device for co-utilizing the headspace in gravity conduits for both gravity flow when it is needed, and conveyance and distribution of recycled water 0—oand captured storm water when it is not.